Scientists solve reproductive riddle

Sperm or eggs?

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For the first time, a research paper describes how the switch between producing a woman's single batch of eggs or a man's lifetime of sperm is flicked.

The discovery, due to be published in the journal Science, could have important applications in fertility treatment.

It makes an interesting aside to a California biotech firm's announcement of a method to produce stem cells from testes.

For women, the meiosis process, which both sexes must carry out to halve their DNA so that a full complement can be regained at fertilisation, all goes on before they're born. Testes don't start producing sperm until years after birth, but go on making fresh ones throughout life.

A team at the University of Queensland has solved the fundamental riddle of how developing foetuses decide which fork in the road to take.

Professor Peter Koopman's group found that a vitamin A derivative triggers the start of meiosis. But in males an enzyme mops up the compound before it can act, suppressing meiosis until after birth.

Professor Koopman said: "It is textbook science and it should provide the basis for a number of practical applications."

As well as the obvious fertility angle, the knowledge could be used to interfere with pest reproduction, or add to the options available to cancer researchers working to beat germ cell tumours, such as testicular cancer. ®